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Drunk or High – It’s Impaired Driving commends The Washington Traffic Safety Commission for its Target Zero campaign and for its first review of marijuana and fatal collisions in Washington State. Washington legalized the adult use of recreational marijuana in 2012. This report demonstrates the impact on traffic safety. In Washington, impaired driving is the leading factor in traffic deaths  - Nearly 60 percent of drivers tested positive for alcohol, marijuana or other drugs (prescription or illegal).

This is the first time in Washington that crash data on marijuana positive drivers has distinguished between drivers who test positive for THC (the impairing substance in marijuana) and those who have residual marijuana (carboxy) in their system from prior use which may have occurred days ago.  Drivers involved in deadly crashes were tested for alcohol and drugs 2010 and 2014. Here are the main takeaways from the report:

  • THC is increasing while alcohol is decreasing (In 2014, the 75 THC-positive drivers comprised the highest number of THC-positive drivers in any year during the five-year period studied. In contract, the 51 drivers over the legal limit who had alcohol only in their systems were the lowest number of such drivers in the study period.
  • Marijuana is the most frequently found drug among drivers in deadly crashes
  • Half of THC positive drivers were above the legal 5 ng/ml limit
  • Most THC positive drivers are young men between 16-25
  • THC positive drivers in deadly crashes were more likely to be involved in daytime crashes
  • Most drivers had multiple substances in their system (34% revealed alcohol only, 8 percent revealed marijuana only)
  • Drivers combining alcohol and marijuana demonstrated increased risk (frequently unbuckled, speeding and unlicensed)
  • Drivers above the legal limit for alcohol (alone or in combination with marijuana/other drugs) in deadly crashes were likely involved in nighttime crashes

The attached table shows the mutually exclusive categories of drivers involved in deadly crashes by toxicology results. The full report, “Driver Toxicology Testing and the Involvement of Marijuana in Fatal Crashes, 2010-2014,” is available at

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Categorization of Drivers Testing Positive for Alcohol, Marijuana or Drugs_Table_Washington State Blog

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